1. Field of the Invention
The present invention relates to the field of analog voltage storage and output devices, and circuits and methods of sensing, storing and outputting analog voltages.
2. Prior Art
In the domain of analog electronics there is often a need for programmable DC analog voltages for system trimming, system control and system parameter setting applications. These voltages typically are set through the use of mechanical trim potentiometers (trim pots) or through digital to analog convertors (DACs) where digital bits are used to set the proper analog voltage storage through some form of digital to analog convertor, or through sample and hold networks for short term analog storage. Most such systems require more than one programmable voltage source, and in fact, some may need more then 100 such as an automatic tester. Some systems go through one time factory programming of these programmable voltage sources, other systems frequently set these voltage sources under user control, and yet other systems routinely perform auto calibration functions under the control of a microprocessor. The programming of the voltage sources are normally performed for various reasons, e.g.: compensating the long term system parameter drift, trimming the manufacturing tolerances of various components of a system in order to achieve optimum system performance or controlling the functionality of the multi-purpose programmable systems.
Mechanical trim potentiometers are bulky and expensive, are sensitive to mechanical vibration and are effected by the high solder temperature they are exposed to during surface mount pc board bonding. Layout of a pc board and packaging also becomes cumbersome, since physical access routes for the mechanical adjustment probes have to be allowed for. Sample and hold networks avoid most of these problems, but have the problem of charge leakage, whereby frequent refreshing is required. Digital storage of analog voltages together with multiple digital to analog convertors when integrated in monolithic form use a lot of silicon real estate, hence, are expensive. Both the sample and hold networks and the digital to analog convertors are volatile voltage sources, in that sample and hold networks have to be refreshed frequently, and the input bits for digital to analog convertors have to be held fixed, respectively. For the multi DAC systems, non-volatility is achieved through the use of some kind of non-volatile storage media (EEPROM, EPROMs, disk, etc. ) to hold the input digital bit status.
What is required is a multi-output programmable non-volatile analog DC voltage source system which is small, is reliable and is a cost effective solution.
U.S. Pat. No. 4,890,259, assigned to the assignee of the present invention, discloses a high density integrated circuit analog signal recording and playback system based on an array storing analog signals. The array has rows and columns of non-volatile memory cells to store the signal information. Analog column read/write circuitry is used to both store the analog information and retrieve it on a real time basis, using interleaving of analog information on a plurality of sample/hold circuits prior to storage in the array to increase throughput.
Recently, the assignee of the present invention introduced a non-volatile analog storage chip of the foregoing type known as the ISD 1016. The single chip ISD 1016 is designed to record and play back analog signals, and includes on-chip, analog signal conditioning circuits and digital control functions to form a complete monolithic recording system in a single 28-pin package. A non-volatile storage array based on production-proven CMOS EEPROM technology stores the sampled signals for 10 or more years without power. The integration of all the components required for recording analog signals is made possible by the significant increase in storage density over digital techniques. For storing, the devices will operable directly from a microphone or similar transducer, and for playback will directly drive a speaker. Full digital addressable messages are easily accessed to provide the capability of constructing messages from stored words, and a plurality of 1016 devices can be connected together for increased storage and playback time.